Developing apparatus

Abstract

A change of a magnetic flux density distribution adjacent to a regulating blade 9 opposed to a developer regulation pole is suppressed at a low cost, while suppressing influence to design latitude of magnetic poles. A position on the outer peripheral surface of the developing sleeve where the magnetic flux density in the normal line direction of the outer peripheral surface of the developing sleeve is a maximum value position. The position on the outer peripheral surface of the developing sleeve 8 corresponding to a center portion position of the half peak range of the magnetic flux density distribution of the developer regulation pole is called half peak center portion. The developer regulation pole is formed such that the maximum value position is deviated not less than 3° in the circumferential direction of the developing sleeve from the half peak center portion position, and the position when the regulating blade 9 opposite is the developing sleeve is in a side of the maximum value position in which the half peak center portion position exists.

The invention claimed is: 
     
       1. A developing apparatus comprising:
 a rotatable developing member configured to carry and feed a developer containing toner and carrier toward a position for developing an electrostatic latent image formed on an image bearing member; 
 a regulating portion provided opposite to said rotatable developing member and configured to regulate an amount of the developer carried on said rotatable developing member, at a position closest to said rotatable developing member; and 
 a magnet provided non-rotatably and stationarily inside said rotatable developing member and provided with a plurality of magnet poles including a magnet pole provided opposite to said regulating portion; 
 wherein a half-peak center portion position, which is a central position of a half-peak width between the half-peak positions of a maximum peak value of a magnetic flux density of said magnetic pole in a normal direction component relative to said rotatable developing member, is not less than 3° upstream of a maximum peak position where the magnetic flux density of said magnetic pole in the normal direction component relative to said rotatable developing member is maximum, with respect to the rotational direction of said rotatable developing member, and 
 wherein a position on said rotatable developing member where said rotatable developing member is closest to said regulating portion is within a range of the half-peak width and upstream of the maximum peak position with respect to the rotational direction of said rotatable developing member. 
 
     
     
       2. An apparatus according to  claim 1 , wherein the half-peak center portion position is not less than 4° upstream of the maximum peak position with respect to the rotational direction of said rotatable developing member. 
     
     
       3. An apparatus according to  claim 1 , wherein the half-peak center portion position is not less than 5° upstream of the maximum peak position with respect to the rotational direction of said rotatable developing member. 
     
     
       4. An apparatus according to  claim 1 , wherein the half-peak center portion position is not less than 3° and not more than 20° upstream of the maximum peak position with respect to the rotational direction of said rotatable developing member. 
     
     
       5. An apparatus according to  claim 1 , wherein the half-peak center portion position is not less than 4° and not more than 20° upstream of the maximum peak position with respect to the rotational direction of said rotatable developing member. 
     
     
       6. An apparatus according to  claim 1 , wherein the half-peak center portion position is not less than 5° and not more than 20° upstream of the maximum peak position with respect to the rotational direction of said rotatable developing member. 
     
     
       7. An apparatus according to  claim 1 , wherein said regulating portion is disposed downstream of a position where the magnetic flux density of said magnetic pole in a tangent line direction component of said rotatable developing member is zero, with respect to the rotational direction of said rotatable developing member. 
     
     
       8. An apparatus according to  claim 1 , wherein said regulating portion is disposed downstream of the half-peak center portion position and upstream of the maximum position with respect to the rotational direction of said rotatable developing member. 
     
     
       9. An apparatus according to  claim 1 , wherein the range of the half-peak width is not more than 70°. 
     
     
       10. An apparatus according to  claim 1 , wherein the range of the half-peak width is not more than 60°. 
     
     
       11. An apparatus according to  claim 1 , wherein the range of the half-peak width is not more than 50°. 
     
     
       12. An apparatus according to  claim 1 , wherein the plurality of magnet poles further includes an upstream magnet pole provided upstream of said magnet pole and adjacent said magnet pole, with respect to the rotational direction of said rotatable developing member, and
 wherein said upstream magnetic pole has the same magnetic polarity as that of said magnetic pole. 
 
     
     
       13. An apparatus according to  claim 1 , wherein the number of magnetic poles is five.